Quantification of uncertainties involved in the conformational study of polymers by light scattering

Gel permeation chromatography (GPC) combined with a multi-angle light scattering (MALS) is a very powerful characterization technique because it provides both absolute molecular weight (Mw) and the radius of gyration (Rg) throughout the separated slices obtained by GPC. This combination of Mw and Rg, can be used to obtain information about the conformation of polymer chains in solutions and the branching of molecules. Due to the interesting properties obtained for polymers, it is essential to quantify the effect of different error sources in light scattering measurements as well as in the data treatment that highly affect the accuracy of obtained molar mass and radius of gyration. Usually, the results obtained for Mw and Rg in this analysis are dispersed for determined ranges of retention time and to have both reliable Rg and Mw for calculation, only high confidence data points have to be chosen. This range is arbitrarily chosen by the user for the data observation. In this work a new method of calculation to obtain Rg and Mw by means of GPC–MALS technique has been developed. As a first point, a data analysis procedure was set in order to describe both Rg and Mw vs. retention time and to determine the range where experimental data are confident. Several aspects in the data analysis have been studied. The polynomial fit function, the influence of the concentration of the sample, the reproducibility of the experiments and the conformational scaling law have been investigated by statistic technique in order to quantify the uncertainties involved.